In small brushes of the generic type, the wire-type segments consist of metal wire, i.e. metal wire coated with plastic or of plasticized metal wire.
These small brushes of the generic type have the disadvantage that there is a risk of rupture of the wire when exposed to alternate bending stresses, i.e. repeated alternate bending. As a rule, there is a risk of rupture already at approximately 20 alternate bending stresses on an average, even wires of 0.20 to 0.50 mm of diameter, although most carefully selected, not taking more than 50 to 60 stresses of this kind.
If the wire of the twisted wire segments breaks off, the user can hurt his mouth and throat during use and there is a risk of swallowing the pieces broken off.
The fiber or bristle segments protruding radially are held by the torque of the twisted wire and may disengage. These disengaged fiber segments can either get stuck or jammed in interdental spaces or gaps, which causes a very unpleasant sensation.
Finally, the wire segments conventionally used can cause galvanic effects when these wires come into contact with fillings. Even a plastic coating cannot prevent such effects completely, as the plastic coating can become cracked during manufacturing or in subsequent treatment, the cracks not being important mechanically, but sufficient to enable a certain electric conductivity in connection with saliva and to make unpleasant galvanic reactions sensible.